(a) Field of the Invention
This invention relates to the field of purification, by ultrafiltration techniques, of dyes useful in foodstuffs.
(b) Information Disclosure Statement
Bollenback et al. U.S. Pat. No. 3,249,444, patented May 3, 1966, describes an ultrafiltration process for increasing the tinctorial power of caramel color in which sugar, i.e. uncaramelized sugar, is separated from caramel color by ultrafiltration through a semi-permeable membrane which permits passage of small, uncolored molecules in solutions containing caramel color and rejects the passage of larger, polymeric caramel color molecules, thus enhancing the color of the concentrate. Preferred membranes for the process are made of vinyl plastics, and preferred pressures are in the range from 20 to 100 p.s.i.g.
Adams et al. U.S. Pat. No. 3,544,455, patented Dec. 1, 1970, discloses a process for the purification of itaconic acid by reverse osmosis through a semi-permeable membrane composed of cellulose acetate or polyamide in which itaconic acid and water are forced to the downstream side of the membrane, while inorganic salts, colored materials and organic materials remain on the upstream side. The process is carried out under a hydrostatic pressure of from 100 to 1,000 p.s.i.g. and at a pH in the range from 2 to 4.
Teed et al. U.S. Pat. No. 4,165,288, patented Aug. 21, 1979, discloses a process for the concentration and partial purification of textile vat dyes for recovery and reuse of the same by subjecting the dye solutions from dyeing operations to reverse osmosis through a semi-permeable membrane, impurities being collected in the permeate and the dye being concentrated in the concentrate. The process is carried out at hydrostatic pressures from 400 to 1,300 p.s.i.g. and at temperatures from 130.degree. F. to 212.degree. F. In order to prevent plugging of the membrane, a turbulent flow of liquid is needed.
EPO Application No. 59,782, published Sept. 15, 1982, discloses a process for concentration, to unspecified levels of purity, of certain anionic dyes, useful in the printing and dyeing of synthetic fibre materials, by passing solutions or suspensions of the dyes through a semi-permeable membrane with a pore diameter of 1-500 Angstroms.
South African Pat. No. 81/6,730, patented Sept. 6, 1982 discloses a process for the preparation of concentrated solutions of anionic dyes, of unspecified purity and useful in printing inks and dye baths, comprising passing a suspension or solution of the dye over a semi-permeable membrane containing ionic groups and having a pore diameter of 1-500 Angstroms.
Osmonics, Inc. Bulletin No. 109 describes the use of a variety of reverse osmosis/ultrafiltration membranes for a variety of purposes, including use of Osmonics, Inc. SEPA-50 membrane in textile dye removal. The membrane is said to give 40-70% sodium chloride rejection and a molecular weight cut-off of approximately 600 for organic materials.
Spatz, Reverse Osmosis/Ultrafiltration Application to Water Reuse and Material Reclamation, May 1, 1975, at page 8, discloses that reverse osmosis/ultrafiltration membranes can be used to remove organic dyes and that some organic dyes are poorly rejected by the membrane. That is, the dye would pass through the membrane.
Spatz, Industrial Wastes, January/February 1974, pages 20-24, discloses the use of reverse osmosis/ultrafiltration membrane methods for concentrating sucrose/dye solutions used in Maraschino cherry processing so that used dyeing solutions, rather than being discarded as in the past, can be concentrated down and reused.
Thus although the general concept of the use of reverse osmosis/ultrafiltration techniques to purify and concentrate a variety of materials is known, so far as is known, the application of this technology to dyes has been restricted to its use for merely concentrating dyes for reuse either in the textile industry, as in Teed or EPO Application No. 59,782, or in Maraschino cherry dyeing, as in Spatz (Industrial Wastes).